Speed Through Water (STW) vs. Speed Over Ground (SOG): Why It Matters for Radar Collision Avoidance? 

This video shows why Speed Through Water (STW) must be set to ship's radar when used for collision avoidance. It also includes a detailed explanation of the difference between Speed Over Ground (SOG) and Speed Through Water(STW).
Speed Over the Ground (SOG) is the speed at which a vessel moves relative to the Earth's surface. It represents the actual speed the vessel is covering over the ground, taking into account all external factors such as currents, and wind.
Speed Through Water (STW) is the speed at which a vessel moves relative to the water it is traveling through. It is not affected by external factors like currents or wind.
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